In large ducts, gate valves are often used for closing the ducts from flow therethrough. Present day gate valves are positioned on one side of the duct, and are moved transversely so they extend entirely across the span of the duct when in a closed position, with the leading edge seating in an end frame. When the duct is conveying hot gases, the large span of the gate can warp, causing proper seating problems in the end frame. Also, when the gases are dust laden, the dust can become trapped in the end frame, preventing proper seating of the gate valve. Further, if there is a need for a concentric pipe, or other central obstruction in the large duct, it is presently impossible to position a gate valve at this location.